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Irradiation-induced voids in alumina single crystal studied by positron annihilation

Nuclear Instruments and Methods in Physics Research Section B Beam Interactions with Materials and Atoms
Publication Date
DOI: 10.1016/0168-583x(94)96228-6
  • Physics


Abstract Angular correlation of annihilation radiation (ACAR) has been measured on α-alumina single crystals irradiated with fast neutrons to a dose of 3 × 10 24 n/m 2 at about 470 K. After post-irradiation annealing above 900 K, remarkable narrowing in ACAR curves has been observed. These ACAR curves can be decomposed into three Gaussian components: a narrow (N), an intermediate (M) and a broad (B) component, with FWHM of 2–5, about 6 and 11 mrad, respectively. The N and M components are attributed to positrons trapped in the voids. A magnetic quenching effect is observed for the N component but not for the M component. This shows that the N component is due to two photon self-annihilation of positronium (Ps) formed in voids. The FWHM of the N component indicates, through the momentum of zero-point motion of Ps, that the average void diameter is 0.6 nm after annealing at 1000 K and 1.7 nm after annealing at 1525 K Striking similarity of the M component to a void-surface trapping component in metallic Al, together with nearly the same lifetime as that of voids in Al, suggests the existence of metallic surface-conduction-electron states in the voids in α-alumina.

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